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  Linear motor actuatorUSPTO Application #: 20060232141Title: Linear motor actuator Abstract: A track rail is formed in a channel-like configuration while having a guide passage for sliders. A table structure that moves within the guide passage includes:a pair of sliders that move forwards and backwards within the guide passage; and a connecting top board connecting those sliders to each other with a predetermined interval therebetween and provided with a mounting surface for a movable member. An armature constituting a linear motor is received between the pair of sliders, and field magnets constituting the linear motor are arranged in the track rail so as to face the guide passage. The armature and the field magnets, which constitute the linear motor, are completely integrated with the table structure and the track rail, which constitute a linear guide, and are entirely contained inside the linear guide. (end of abstract) Agent: Westerman, Hattori, Daniels & Adrian, LLP - Washington, DC, US Inventors: Akihiro Teramachi, Toshiyuki Aso, Yoshinobu Tanaka, Hiroshi Kaneshige, Yuaniun Xu USPTO Applicaton #: 20060232141 - Class: 310012000 (USPTO) The Patent Description & Claims data below is from USPTO Patent Application 20060232141. Brief Patent Description - Full Patent Description - Patent Application Claims
TECHNICAL FIELD [0001] The present invention relates to a linear motor actuator which supports a movable member such as a table on a stationary portion such as a bed by using a linear guide so that the movable member is free to reciprocate, the linear motor actuator being capable of repeatedly positioning the movable member with respect to the stationary portion by utilizing a propulsion force or brake force generated by a linear motor. More specifically, the present invention relates to an improvement for integrating the linear motor and the linear guide in a compact manner. BACKGROUND ART [0002] Linear actuators, which impart linear motion to a movable member such as a table and cause the movable member to stop at a predetermined position, are frequently used for various kinds of tables of machine tools, the moving portion of industrial robots, various kinds of conveying devices, and the like. Conventionally, with respect to the linear actuators of this type, known examples of driving means for imparting a propulsion force or brake force to the movable member include one which converts the rotation of a motor into linear motion by using a ball screw and one which converts the rotation of a motor into linear motion by using an endless timing belt wound around a pair of pulleys. Recent years have seen the appearance of various types of actuators employing a linear motor as drive means, that is, linear, motor actuators. [0003] As the most common type of linear motor actuators, there is known one in which the movable member is supported on a stationary portion such as a bed or a column by using a pair of linear guides so that the movable member is free to reciprocate, and in which a stator and a mover that constitute a linear motor are respectively mounted to the stationary portion and the movable member so as to be opposed to each other (JP 10-290560A and the like). Specifically, a track rail of each linear guide is arranged in the stationary portion and the stator of the linear motor is mounted in parallel to the track rail, and a slider of the linear guide and the mover of the linear motor are mounted to the movable member; by incorporating the slider on the movable member side into the track rail, the movable member is supported on the stationary member so as to freely reciprocate, and the stator on the stationary portion side and the mover on the movable member side are opposed to each other. [0004] With linear motor actuators, the parallelism between the track rail of the linear guide and the stator of the linear motor is important in securing the accuracy of the movement of the movable member, and it is also important, for the purpose of attaining a sufficient propulsion force, that the stator and mover of the linear motor be opposed to each other through a predetermined air gap. However, in the case of the linear motor actuators whose linear guide and linear motor are completely separated from each other as described above, it is extremely difficult and troublesome to perform the assembly while taking the above requirements into consideration. [0005] Typical examples of linear motors include so-called synchronous motors composed of a field magnet employing a permanent magnet and of an armature around which a coil is wound. As the synchronous motors, there exist those of a core-attached type having a core formed of a magnetic member and those of a core-less type with no such core attached. Although the core-attached type ones prove effective from the viewpoint of obtaining a large propulsion force, due to the existence of the core, a magnetic attraction force equivalent to several times of the propulsion force is exerted between the armature and the field magnet even when no electric current is passed through the armature. For this reason, the above-mentioned assembly operation becomes even more difficult in the case where such a core-attached type linear motor is adopted. [0006] On the other hand, known examples of linear motor actuators in which the linear guide and the linear motor are integrated together include those disclosed in JP 05-227729 A and JP 2001-25229 A. In the linear motor actuator of the former type disclosed in JP 05-227729 A, a recessed groove is formed in the track rail along the longitudinal direction thereof, with the armature being received within the recessed groove, and the slider is formed in a saddle-like configuration straddling the track rail. In the slider, the field magnet is fixed at a position opposed to the armature on the track rail side; when electric current is passed through the armature, a propulsion force is exerted on the slider incorporating the field magnet due to the Fleming's left-hand rule, so the slider moves along the track rail. That is, this linear motor actuator is a movable magnet type linear motor actuator having the field magnet as a mover. [0007] However, with the movable magnet type linear motor actuator, the armature must be provided over the entire length of the track rail, and in order to set the resolution of the actuator with high accuracy, the armature coil must be finely segmented. Accordingly, when a large stroke length is set for the slider, this not only makes the preparation of the armature coil rather troublesome but also causes an increase in cost. [0008] In contrast, the linear motor actuator of the latter type disclosed in JP 2001-25229 A is a so-called movable coil type one in which the armature moves together with the slider. That is, the field magnet is directly fixed to the track rail of the linear guide, and the armature is mounted in the slider; when electric current is passed through the armature to excite the armature coil, the slider incorporating the armature moves along the track rail. [0009] However, with the above linear motor actuator, although the armature and the field magnet are fixed to the slider and track rail of the linear guide, respectively, they are externally fixed without being incorporated in the track rail and the slider, so the size of the actuator itself disadvantageously increases. Further, there is a risk that the field magnet or the armature may come into contact with peripheral equipment during the transport operation or the mounting operation thereof to the stationary portion such as a bed, resulting in damage. DISCLOSURE OF THE INVENTION [0010] The present invention has been made in view of the problems as described above, and it is an object of the present invention to provide a linear motor actuator which is capable of imparting a large propulsion force to a movable member such as a table and which achieves a compact construction by integrating a linear guide and a linear motor together, thereby enabling manufacture at low cost as well as ease of handling. [0011] To attain the above object, a linear motor actuator according to the present invention includes: a track rail having a stationary base portion and a pair of side wall portions extending upright from the stationary base portion, the track rail being formed in a channel-like configuration including a guide passage surrounded by the stationary base portion and the side wall portions, the side wall portions each being provided with a ball rolling groove facing the guide passage; a table structure including a large number of balls that roll in the ball rolling groove, and an endless circulation passage in which the balls circulate, the table structure being mounted between the pair of side wall portions of the track rail through the balls to freely move within the guide passage; a field magnet fixed to the track rail and having N poles and S poles alternately arranged along a longitudinal direction of the track rail; and an armature mounted to the table structure such that the armature is opposed to the field magnet, the armature constituting a linear motor together with the field magnet and exerting on the table structure a propulsion force or a brake force acting in the longitudinal direction of the track rail. [0012] The table structure includes: a pair of sliders each including the endless circulation passage for the balls and moving forwards and backwards within the guide passage of the track rail; and a connecting top board connecting the sliders to each other with a predetermined interval between the sliders and provided with a mounting surface for a movable member. Because the pair of sliders are connected to each other with an interval therebetween by the connecting top board, a space is formed between those sliders in the guide passage of the track rail. This space serves as the space for receiving the armature. Further, the armature is located within the guide passage of the track rail while being fixed to the connecting top board at a position between the pair of sliders, and includes an armature core of a comb tooth-like configuration and a coil, the armature core having a plurality of slots and teeth formed at a predetermined pitch along the longitudinal direction of the track rail, the coil being wound around each of the teeth of the armature core so as to fill in each slot. That is, the armature is placed within the guide passage of the track rail while being suspended from the connecting top board. In other words, the connecting top board connecting the pair of sliders to each other serves as a lid for the guide passage, whereby the armature is enclosed within the guide passage. That is, according to the structure adopted by the present invention, the armature that constitutes the linear motor is entirely received within the guide passage of the track rail and no portion of the armature is exposed to the outside. Further, the field magnet that constitutes, together with the armature, the linear motor is disposed at the position opposed to the armature core fixed to the connecting top board, with the stationary base portion of the track rail serving as the yoke of the field magnet. Accordingly, in the linear motor actuator according to the present invention, the armature and the field magnet, which constitute the linear motor, are completely integrated with the table structure and the track rail, which constitute the linear guide, and are entirely contained inside the linear guide, thereby achieving an extremely compact construction. Further, there is no fear of the linear motor being exposed to the outside of the track rail formed in a channel-like configuration, thereby achieving extreme ease of handling during the transport or mounting operation. [0013] Further, the armature is directly connected to the connecting top board of the table structure, and the field magnet is simply disposed on the stationary base portion of the track rail. Accordingly, there is no need to provide any special bracket or the like for mounting those components to the table structure and the track rail, thereby achieving manufacture at extremely low cost. [0014] Further, with the linear motor actuator according to the present invention, the interval between the pair of sliders can be arbitrarily set by changing the length of the connecting top board as appropriate. Accordingly, depending on the intended application, the number of the armatures to be placed in the longitudinal direction of the track rail can be changed as appropriate in order to secure the propulsion force required for the table structure, thereby making it possible to flexibly cope with the excess/deficiency of the propulsion force for the table structure. [0015] In order to secure sufficient propulsion and brake forces to be imparted to the table structure, the armature is equipped with the armature core formed of a magnetic member. The armature core has the plurality of slots and teeth formed alternately at a predetermined pitch along the longitudinal direction of the track rail, that is, in the direction in which the table structure moves. As a conceivable example of the formation pitch of those teeth, assuming that the repeating cycle of the magnetic poles in the field magnet is .lamda., the formation pitch may be set to .lamda.n/4 (n is an integer) On the other hand, since they support the movable member such as a table while moving within the guide passage of the track rail, the pair of sliders constituting the table structure must have a high rigidity, and as such, are usually formed of a metal material. For this reason, when the field magnet is provided so as to face the guide passage of the track rail, the magnetic force of the field magnet is exerted on the sliders, with the result that a resistance acts intermittently with respect to the movement of the sliders as the sliders are moved within the guide passage. This phenomenon is called cogging, which occurs due to the positional relation between the plurality of magnetic poles, which are arranged in the field magnet, and the sliders. When such cogging exerts a large influence, the moving speed or acceleration of the table structure changes, and the accuracy of the stopping position of the table structure is also affected. Therefore, it is necessary to make such cogging as small as possible. In view of this, it is preferable to form in the lower surface of each slider, that is, in the surface thereof opposed to the stationary base portion of the track rail, a plurality of slots and teeth alternately along the movement direction of the slider, thus forming the above surface in a comb-tooth like configuration as a whole. When such slots and teeth are formed in each of the sliders, by adjusting the formation pitch thereof, the magnetic force exerted by the field magnet to attract the sliders in the movement direction thereof can be substantially, if not totally, canceled out, thereby making it possible to reduce the occurrence of the cogging. [0016] At this time, the formation pitch of the slots and teeth in the sliders may be adjusted as appropriate. In this regard, since the formation pitch of the slots and teeth formed in the armature core is also set so as to suppress the cogging, it is preferable, like the formation pitch of the slots and teeth in the armature core, to set the formation pitch of the slots and teeth in the sliders to .lamda.n/4 (n is an integer) and to arrange the teeth of the sliders adjacent to the teeth of the armature core in the lateral direction. [0017] Even when the formation pitch of the slots and teeth in the armature core is set to .lamda.n/4 (n is an integer), cogging that results from the positional relation between the armature core and the field magnet cannot be completely eliminated. In addition, as described above, cogging occurs in the sliders themselves due to the positional relation between them and the field magnet. In view of this, it is preferable that fixing means for fixing the sliders to the connecting top board be capable of freely changing a fixing position of the sliders to the connecting top board along the direction in which the table structure moves. With this construction, by performing fine adjustment on the fixing position of the armature with respect to the connecting top board along the movement direction of the table structure, it is possible to find the fixing position where the cogging that occurs due to the sliders and the cogging that occurs due to the armature core are canceled by each other. By fixing the armature to the connecting top board at such a position, cogging that occurs upon incorporating the linear motor into the linear guide can be almost entirely eliminated. [0018] As described above, with the linear motor actuator according to the present invention, the armature and the field magnet, which constitute the linear motor, are completely integrated with the sliders and the track rail, which constitute the linear guide, and are entirely contained inside the linear guide, thereby achieving an extremely compact construction. Further, there is no fear of the linear motor being exposed to the outside of the track rail formed in a channel-like configuration, thereby achieving extreme ease of handling during the transportor mounting operation. Further, the armature is directly connected to the connecting top board of the table structure, and the field magnet is simply disposed on the stationary base portion of the track rail. Accordingly, there is no need to provide any special bracket or the like for mounting those components to the table structure and the track rail, thereby achieving manufacture at extremely low cost. BRIEF DESCRIPTION OF THE DRAWINGS [0019] FIG. 1 is a perspective view showing a linear motor actuator according to a first embodiment of the present invention. [0020] FIG. 2 is a sectional view taken along the line II-II of FIG. 1. Continue reading... Full patent description for Linear motor actuator Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Linear motor actuator patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. Each week you receive an email with patent applications related to your keywords. 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